Say on Shells, &c. 39 
undergone much apparent change, excepting that the lamel- 
lary increments are readily popaante and very friable, the 
epidermis also is wanting. 
Ti is the same species of shell as that described and figur- 
ed by Collini in his Journal p. 10, pl. 6. fig. 1. under the 
name of Ostrewm polyleptoginglimum ; ; and also anonymous- 
ly, by Parkinson Organ. Rem. vol. 3, pl. 
The teeth of one specimen, in the possession of the 
Academy of Natural Sciences, are obsolete. 
Collini. says, it is often perforated by sea insects ; our 
specimens are also penetrated, but the cavities are formed 
by an ampullaceous Pholas, which in reality may be the 
same as those which that author alludes to, by the term sea 
insects ; it may be thus named and described. 
Pholas ovalis. 
Tube equal, entire and rounded at base, and gradually 
attenuated towards the anterior termination. Shell subo- 
vate, dehiscent ; valves with crowded, acute, elevated, trans- 
verse lines, somewhat decussate with longitudinal slightly 
indented ones, a more conspicuous, longitudinal, indented 
line before the middle, posterior basal margin smooth ; 
within equal, the posterior basal margin distinguished by a 
slight undulation. 
‘This is not, strictly speaking, a Pholas, inasmuch as it is 
included in a tube; but in other respects it corresponds 
very well with the species of that genus, as far as I canjudge 
from incomplete specimens, not having seen the accessory 
valves. It will not agree with Teredina Lam. as its valves 
are concealed by the tube ; by which character it is assim- 
lated to Fistulana, but from this genus also, it is distinguish- 
able, by the form of its valves, and most probably, by being 
destitute of the anterior, crustaceous, branchial appendages 
or valvules, though it is proper to observe that the anterior 
extremities of the tubes (which contain these parts in fistu- 
lana, teredo, &c.) are deficient in my specimens of P. ovalis. 
In the somewhat compact earth which was included be- 
tween two fragments of the valves of the abovementioned 
Perna, were a Tew interesting shells, some of which are per- 
fectly firm and entire, others, although to all appearance 
similarly circumstanced, are extremely friable, and even 
